1. Echinomastus johnsonii (Parry ex Engelmann) E. M. Baxter, Calif. Cact. 75. 1935.
Echinocactus johnsonii Parry ex Engelmann in S. Watson, Botany (Fortieth Parallel), 117. 1871 (as johnsoni); Echinomastus johnsonii var. lutescens (Parish) Wiggins; Neolloydia johnsonii (Parry ex Engelmann) L. D. Benson; Sclerocactus johnsonii (Parry ex Engelmann) N. P. Taylor
Stems 10-25 × 7-15 cm; ribs (13-)18-21; areoles (14-)21-26 mm apart along ribs; areolar glands present at least seasonally. Spines 13-24 per areole, pale yellow to grayish lavender to maroon; radial spines 9-16 per areole; abaxial (shortest) radial spine 6-19 × (0.2-)0.4-0.6 mm; adaxial and lateral (longest) radial spines ca. 27-40 mm; central spines 4-9 per areole, present at all ages, 27-41 × (0.7-)1.1-1.4 mm; longest central spine straight to strongly decurved; abaxial central spine porrect, ca. 27-40 mm Flowers 4-6.5 × 4-7.7 cm; inner tepals yellow or pink to magenta, basal portions blotched with maroon , 2.5-3.7 × 1-1.8 cm; stigma lobes yellowish white to green. Fruits dehiscent only along single, longitudinal split, ± spheric, 17-18 mm. 2n = 22.
Flowering (Feb-)Mar-May; fruiting Apr-Jun. Mojave desert scrub and upper edge of Sonoran desert scrub, rocky slopes, gravelly hills; 500-1400 m; Ariz., Calif., Nev., Utah.
Echinomastus johnsonii varies geographically in both flower and spine color. The yellow-flowered plants have been named E. johnsonii var. lutescens. The pink-flowered plants occur in separate populations, as far as is known, to the north of the yellow-flowered plants, but the interface between the two forms is poorly understood.